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Topic: Bosch SHU9925 Dishwasher Not Using Same Water through entire cycle (Read 15009 times)

I have an update. And BTW, like I said earlier, I always keep the sump clean. And in this case, the sump was spotless and the impeller is fine. I'm not trying to be a jerk. Its just that this is the third forum I've gotten on looking for help and every time I keep hearing "clean out the sump" as if that is all anyone knows about. I'm not trying to put you down as I see you have a pretty good reputation. But lets get past the sump.

Here's what I've come to learn.

I tore apart the water distribution system. On top of that distribution system is the water inlet switch. It is a pressure operated diaphram. As the water level rises air is pushed up into the thing and a diaphram pushes out on an actuating rod that clicks a switch. The first time the switch clicks the washer starts running and the water level drops. It continues to allow water into the tub and the second time it clicks water flow into the unit is stopped.

The red thing I spoke about earlier does not control the drain pump. It is an overflow device. After the washer was running I took and poured a gallon or so of water into it which made the float rise and start the pump. Once the float dropped to the proper level the drain pump stopped.

I then sat there and watched the stupid thing. Great way to spend a Saturday eh? When the pre-wash stage ended the pump kicked on and drained like a banshee. It drained for a good 30 seconds like the book says it should. When that finished I opened the door and it was empty. After closing the door it started filling once more with clean water.

So I'm stumped. This time all worked well. Last time it didn't. This is what I mean by intermittent. I didn't fix or clean anything. All I did was

disconnect the plugs to the fill switch and overflow draim pump switch

take apart the input control thingy (to understand what it did)

put it all back together and run it again

That's it. So what controls the pump at the end of the three stages? Whatever does that is the culprit. Either that or the impeller sometimes just can't pump. But I don't think its the impeller. It spun just fine and the problem is that it can't pump, its that it doesn't pump for very long.

Sorry about that first paragraph on my last post. It reads like I am being a jerk. I meant no offense. But the one thing I have always checked first has been the sump. We have had this unit for about 5 years and in the past everytime the dishes had that grainy feel to them it was because there was a small item stuck down in one of the sump tines. Some of the things I've found in there were a kernel of corn, a pea, a small piece of sausage, some sunflower seeds. Every time I'd remove it and re-run it and all would be good. So when it comes to the sulmp, I've become a sort of expert at cleaning it out. My wife has been complaining about this thing for a couple months now and the difference has been that many times I haven't found anything in the sump which is why I'm wasting my Saturday laying on the kitchen floor staring at the bowels of our dishwasher. Not that I'm complaining, I kinda like how this thing is designed and its pretty cool to learn how these things work.

And JW, I appreciate you using some of your Saturday to pitch in and help. I have another question though. Do you have any idea why the micro-filter on these units allows things like corn kernels and the like to get down through it? The down tube of the filter has two baffles in it that will let things fall through. It just seems counter intuitive to me that a filter actually has a way through it.

Update: Ran it twice today using the rinse only cycle. It did not drain either time. I scooped out all the water, removed the sump cover and there wasn't anything I could see in there . The impeller moves fine. So I stuck my finger into the drain hole and felt something. I used a hook shaped wire to grab it and lo and behold I start pulling out some sort of round rubber thingy about the size of the drain hole. I was about to yank it out until I realized that it just so happened to be the size of the hole. Is this thing supposed to be there? It is attached and I'd have to rip it out. The only thing I figure it could be is a type of check valve so that water doesn't come back in to the unit. The schematic I have doesn't show it.

It took me a while but I finally figured out the schematic. The drain pump is operated by 2 things. One is the overfill switch (which works fine) and the other is the control unit. It pumps just fine anytime I engage the overfill switch. It does not always work fine when it is suposed to empty the unit after a clean stage. Does this mean the controller is shot, or maybe somewhere wires connect between the controller and the pump?

I got it working. Before putting in a new motherboard I made sure the connections were good. I disconnected and re-connected the plugs at the motherboard and then down in the base of the machine where the harness from the motherboard plugs into the junction block to all the components. It started working fine again. Then about two weeks ago the dishes were sometimes slightly dirty with dirty water in the base of the unit. It turns out that the air gap was full of crud. Now she cleans like she did day 1.

My wife and I have 4 kids and this unit runs at least 5 times a week, sometimes twice in a day and it still cleans superbly. It has been a great piece of machinery. And it's quiet.